Classifications

• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
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  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
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  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
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  • H01M10/0566—Liquid materials
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  • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
  • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
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  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
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  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/381—Alkaline or alkaline earth metals elements
  • H01M4/382—Lithium
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  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/40—Alloys based on alkali metals
  • H01M4/405—Alloys based on lithium
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  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/581—Chalcogenides or intercalation compounds thereof
  • H01M4/5815—Sulfides
• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/624—Electric conductive fillers
  • H01M4/625—Carbon or graphite
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/44—Fibrous material
• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/027—Negative electrodes
• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0017—Non-aqueous electrolytes
  • H01M2300/0025—Organic electrolyte
  • H01M2300/0028—Organic electrolyte characterised by the solvent
• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0402—Methods of deposition of the material
  • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
• • H—ELECTRICITY
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  • H01M4/04—Processes of manufacture in general
  • H01M4/043—Processes of manufacture in general involving compressing or compaction
  • H01M4/0435—Rolling or calendering
• • H—ELECTRICITY
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  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
  • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
  • H01M50/417—Polyolefins
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
  • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
  • H01M50/423—Polyamide resins
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  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
  • H01M50/491—Porosity
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to a lithium-sulphur cell.
• the present invention also relates to the use of a tetrafluoroborate salt as an additive for enhancing the cycle life of a lithium-sulphur battery.
• the present invention relates to an electrolyte for a lithium sulphur cell.
• a typical lithium-sulphur cell comprises an anode (negative electrode) formed from lithium metal or a lithium metal alloy, and a cathode (positive electrode) formed from elemental sulphur or other electroactive sulphur material.
• the sulphur or other electroactive sulphur-containing material may be mixed with an electrically conductive material, such as carbon, to improve its electrical conductivity.
• the carbon and sulphur are ground and then mixed with a solvent and binder to form a slurry.
• the slurry is applied to a current collector and then dried to remove the solvent.
• the resulting structure is calendared to form a composite structure, which is cut into the desired shape to form a cathode.
• a separator is placed on the cathode and a lithium anode placed on the separator. Electrolyte is introduced into the cell to wet the cathode and separator.
• Lithium-sulphur cells are secondary cells, and may be recharged by applying an external current to the cell. Rechargeable cells of this type have a wide range of potential applications. One important consideration when developing lithium-sulphur secondary cells is maximising the useful cycle life of the cell.
• the sulphur in the cathode is reduced in two-stages.
• the sulphur e.g. elemental sulphur
• polysulphide species S n 2" (n ⁇ 2).
• the polysulphide species are reduced to lithium sulphide, Li 2 S, which, typically, deposits on the surface of the anode.
• the two-stage mechanism typically occurs in reverse, with the lithium sulphide being oxidised to lithium polysulphide and thereafter to lithium and sulphur.
• the polysulphide species it is desirable for the polysulphide species to be soluble in the electrolyte as this increases the utilisation of the electroactive material during discharge. Without the polysulphides dissolution, the reduction of electroactive sulphur may be constrained to the carbon-sulphur interface, resulting in relatively low cell capacities.
• the electrolyte of a lithium sulphur cell typically comprises an electrolyte salt and an organic solvent.
• Suitable electrolyte salts include lithium salts. Examples include lithium hexafluorophosphate (LiPF 6 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium perchlorate (LiCI0 4 ), lithium trifluoromethanesulfonimide (LiN(CF 3 S0 2 )2) and lithium l trifluoromethanesulphonate (CF 3 S0 3 Li).
• Such lithium salts provide charge carrying species in the electrolyte, allowing the redox reactions at the electrodes to occur.
• Lithium tetrafluoroborate (LiBF 4 ) is a lithium salt that has be used as an electrolyte salt in lithium-ion cells.
• lithium tetrafluoroborate is unsuitable as an electrolyte salt because it reacts with lithium polysulphides as follows:
• a lithium-sulphur cell comprising
• an anode comprising lithium metal or lithium metal alloy
• a cathode comprising a mixture of electroactive sulphur material and solid electroconductive material
• an electrolyte comprising a tetrafluoroborate salt and an organic solvent, wherein the tetrafluoroborate salt is present in the electrolyte at a concentration of 0.05 to 0.5M, and
• tetrafluoroborate salt is present in an amount, wherein the molar ratio of tetrafluoroborate anion, BF 4 " , to sulphur, S, in the electroactive material is 0.009 - 0.09 : 1.
• the present invention also provides the use of a tetrafluoroborate salt as an additive for enhancing the cycle life of a lithium sulphur battery.
• a tetrafluoroborate salt can be used as an additive to enhance the cycle life of a lithium sulphur battery.
• the tetrafluoroborate anions are believed to solvate the polysulphides formed upon discharge, enhancing their solubility in the electrolyte. This increases the utilisation of the electroactive material during discharge. Without the polysulphides dissolution, the reduction of electroactive sulphur may only occur at the carbon-sulphur interface, resulting in relatively low cell capacities.
• Suitable tetrafluoroborate salt may be used.
• Suitable salts include metal salts and/or ammonium salts.
• Suitable metal salts include alkali metal salts including salts of potassium, sodium and lithium.
• lithium tetrafluoroborate is employed.
• Suitable ammonium salts include tetra alkyl ammonium salts. Examples include tetraethyl ammonium salts and tetramethyl ammonium salts.
• the tetrafluoroborate salt may be present in the electrolyte at a concentration of 0.05 to 0.5M.
• the tetrafluoroborate salt concentration should preferably be sufficient to provide an appreciable improvement in cycle life. However, it should preferably not be too high as to give rise to undesirable side reactions. Without wishing to be bound by any theory, it is believed that, at concentrations significantly above 0.5M, the tetrafluoroborate may react with polysulphide species in undesirable side reactions.
• An example of such an undesirable side reaction is as follows:
• the tetrafluoroborate salt is present in the electrolyte at a concentration of 0.1 to 0.4M, more preferably, 0.2 to 0.3 M, for example, about 0.3 M.
• the tetrafluoroborate salt When used in a lithium sulphur cell, the tetrafluoroborate salt is present in an amount, wherein the molar ratio of tetrafluoroborate anion, BF 4 " , to sulphur, S, in the electroactive material is 0.009 - 0.09 : 1 , preferably, 0.01 - 0.09 : 1 , more preferably, 0.02 0.09 : 1.
• the molar ratio of tetrafluoroborate anion, BF 4 " , to sulphur, S, in the electroactive material is 0.03 - 0.08 : 1 , more preferably, 0.04 - 0.07 : 1 , for example, 0.05 - 0.07 : 1.
• the molar ratio of tetrafluoroborate anion, BF 4 " , to sulphur, S, in the electroactive material is 0.06 : 1.
• the molar ratio is calculated on the basis of the number of moles of BF 4 " anion in the electrolyte and the number of moles of sulphur (S) in the electroactive material. Accordingly, where the electroactive material does not consist solely of sulphur, the number of moles of sulphur (S) in the electroactive material will be less than the number of moles of electroactive material.
• the electrolyte may comprise a further electrolyte salt (i.e. one that is provided in addition to the tetrafluoroborate salt).
• the further electrolyte salt is preferably a lithium salt, (i.e. a lithium salt that is not lithium tetrafluoroborate).
• Suitable lithium salts include lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium
• the lithium salt is lithium trifluoromethanesulphonate.
• the further electrolyte salt may be present in the electrolyte at a concentration of 0.1 to 5M, preferably, 0.5 to 3M, for example, 1 M.
• the further electrolyte salt is a lithium salt that is present in the electrolyte at a concentration that is 50% to 100% of the saturation concentration of the lithium salt in the electrolyte or electrolyte solvent.
• the lithium salt may be present at a concentration that is 70% to 100% of the saturation concentration, more preferably 80% to 100% of the saturation concentration, for example, 90% to 100% of the saturation concentration.
• the molar concentration of tetrafluoroborate salt may be less than 90%, preferably, less than 80%, more preferably less than 70%, yet more preferably less than 60%, for example, less than 50% of the molar concentration of the further electrolyte salt.
• the molar concentration of tetrafluoroborate salt may be less than 40%, for example, less than 30% of the molar concentration of the further electrolyte salt.
• the molar concentration of the tetrafluoroborate salt may be more than 1 %, preferably, more than 5%, for example, more than 10% of the molar concentration of the further electrolyte salt.
• the molar concentration of tetrafluoroborate salt may be 1 to 40%, preferably, 5 to 30%, for instance, 10 to 20% of the molar concentration of the further electrolyte salt.
• the present invention provides an electrolyte for a lithium sulphur cell, said electrolyte comprising
• lithium salt selected from at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium trifluoromethanesulfonimide and lithium trifluoromethanesulphonate,
• tetrafluoroborate salt is present in the electrolyte at a concentration of 0.05 to 0.5M
• lithium salt is present in the electrolyte at a concentration that is 50% to 100% of the saturation concentration of the lithium salt in the electrolyte.
• a lithium-sulphur electrochemical cell comprising: an anode comprising lithium metal or lithium metal alloy; a cathode comprising a mixture of electroactive sulphur material and solid electroconductive material; a porous separator; and an electrolyte comprising at least one lithium salt, at least one organic solvent and a surfactant.
• the electrochemical cell of the present invention may be any suitable lithium- sulphur cell.
• the cell typically includes an anode, a cathode, an electrolyte and, preferably, a porous separator, which may advantageously be positioned between the anode and the cathode.
• the anode may be formed of lithium metal or a lithium metal alloy.
• the anode is a metal foil electrode, such as a lithium foil electrode.
• the lithium foil may be formed of lithium metal or lithium metal alloy.
• the cathode of the electrochemical cell includes a mixture of electroactive sulphur material and electroconductive material. This mixture forms an electroactive layer, which may be placed in contact with a current collector.
• the electroactive sulphur material may comprise elemental sulphur, sulphur-based organic compounds, sulphur-based inorganic compounds and sulphur-containing polymers.
• elemental sulphur is used.
• the solid electroconductive material may be any suitable conductive material.
• this solid electroconductive material may be formed of carbon. Examples include carbon black, carbon fibre, graphene and carbon nanotubes. Other suitable materials include metal (e.g. flakes, filings and powders) and conductive polymers. Preferably, carbon black is employed.
• the mixture of electroactive sulphur material and electroconductive material may be applied to the current collector in the form of a slurry in a solvent (e.g. water or an organic solvent).
• a solvent e.g. water or an organic solvent.
• the solvent may then be removed and the resulting structure calendared to form a composite structure, which may be cut into the desired shape to form a cathode.
• a separator may be placed on the cathode and a lithium anode placed on the separator.
• Electrolyte may then be introduced into the assembled cell to wet the cathode and separator.
• the electrolyte may be applied to the separator, for example, by coating or spraying before the lithium anode is placed on the separator.
• the cell comprises an electrolyte.
• the electrolyte is present or disposed between the electrodes, allowing charge to be transferred between the anode and cathode.
• the electrolyte wets the pores of the cathode as well as the pores of the separator.
• Suitable organic solvents for use in the electrolyte are tetrahydrofurane, 2- methyltetrahydrofurane, dimethylcarbonate, diethylcarbonate, ethylmethylcarbonate, methylpropylcarbonate, methylpropylpropionate, ethylpropylpropionate, methyl acetate, dimethoxyethane, 1 , 3-dioxolane, diglyme (2-methoxyethyl ether), tetraglyme, ethylene carbonate, propylene carbonate, butyrolactone, dioxolane, hexamethyl phosphoamide, pyridine, dimethyl sulfoxide, tributyl phosphate, trimethyl phosphate, N, N, N, N-tetraethyl sulfamide, and sulfone and their mixtures.
• the organic solvent is a sulfone or a mixture of sulfones.
• sulfones are dimethyl sulfone and sulfolane.
• Sulfolane may be employed as the sole solvent or in combination, for example, with other sulfones.
• the electrolyte comprises lithium trifluoromethanesulphonate and sulfolane.
• the tetrafluoroborate anion advantageously solvates the polysulphides, increasing their solubility in the electrolyte.
• the separator may comprise any suitable porous substrate that allows ions to move between the electrodes of the cell.
• the separator should be positioned between the electrodes to prevent direct contact between the electrodes.
• the porosity of the substrate should be at least 30%, preferably at least 50%, for example, above 60%.
• Suitable separators include a mesh formed of a polymeric material. Suitable polymers include polypropylene, nylon and polyethylene. Non-woven polypropylene is particularly preferred. It is possible for a multi- layered separator to be employed.
• Example 1 [0027] In this Example, an electrolyte comprising 1 M lithium triflate in sulfolane was used as a reference electrolyte in a lithium-sulphur cell. The discharge capacity of this reference cell was determined over approximately 140 cycles. A further cell was produced in the same manner except that lithium tetrafluoroborate was added to the reference electrolyte to form a 0.1 M LiBF 4 solution in the electrolyte. The discharge capacities of the cells were determined over approximately 140 cycles. As can be seen from Figure 1 , the rate of capacity fade is reduced by the addition of the tetrafluoroborate salt. In this Example, the ratio of tetrafluoroborate anion, BF 4 " , to S in the electroactive material was 0.01875: 1.
• Example 2 a further cell was produced in the same manner as the reference cell of Example 1 except that lithium tetrafluoroborate was added to the reference electrolyte to form a 0.05M LiBF 4 solution in the electrolyte.
• the discharge capacity of the cell was determined over approximately 60 cycles. These discharge capacities were compared with the discharge capacity of the reference cell. As can be seen from Figure 2, with the addition of the tetrafluoroborate salt, an improvement in capacity fade can be observed after approximately 35 cycles.
• the ratio of tetrafluoroborate anion, BF 4 " to S in the electroactive material was 0.0093:1.
• Example 2 a further cell was produced in the same manner as the reference cell of Example 1 except that tetraethyl ammonium tetrafluoroborate was added to the reference electrolyte to form a 0.05M TEABF 4 solution in the electrolyte.
• the discharge capacity of the cell was determined over 50 + cycles. These discharge capacities were compared with the discharge capacity of the reference cell. As can be seen from Figure 6, with the addition of the tetrafluoroborate salt, an improvement in capacity fade is observed.
• the ratio of tetrafluoroborate anion, BF 4 " to S in the electroactive material was 0.0093:1.
• Example 3 a further cell was produced in the same manner as the reference cell of Example 1 except that an electrolyte comprising 1.25M lithium triflate in sulfolane was used. The discharge capacity of the cell was determined over 50 + cycles. These discharge capacities were compared with the discharge capacity of the reference cell and the cell of Example 3 (1 M lithium triflate + 0.2M LiBF 4 ). As can be seen from Figure 7, the cell formed using an electrolyte comprising 1.25M lithium triflate performed significantly worse than a cell formed using an electrolyte comprising 1 M lithium triflate + 0.2M LiBF 4 despite the overall lithium salt concentrations in the electrolyte being comparable. The addition of 0.2M LiBF 4 to the electrolyte significantly improved the cell's resistance to capacity fade.

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• 2014
  • 2014-12-16 CN CN201480068250.7A patent/CN105830258A/zh active Pending
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  • 2014-12-16 TW TW103143836A patent/TW201539847A/zh unknown
  • 2014-12-16 JP JP2016540690A patent/JP2017504155A/ja active Pending
  • 2014-12-16 US US15/102,106 patent/US20160315350A1/en not_active Abandoned
  • 2014-12-16 WO PCT/GB2014/053719 patent/WO2015092384A1/en not_active Ceased
  • 2014-12-16 CA CA2932973A patent/CA2932973A1/en not_active Abandoned

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